don wareham – field application engineer · don wareham – field application engineer ... design...
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Step Voltage Regulators
Don Wareham – Field Application Engineer
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Today’s Agenda
• Introduction • Voltage Regulator theory • Voltage Regulator application considerations • Installation and proper bypassing • Wrap-up/questions
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TRANS- FORMER
End of line
Volta
ge
Distance
VLD = Voltage drop due to line losses
VLD
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Regulator Theory – Purpose • Why is voltage regulation needed?
• Power quality criteria requires a constant voltage despite variations in load current
• Load current variations are due to: • New loads • Load profiles – Daily and Seasonal
CURRENT
TIME OF DAY 12am 6am 12pm 6pm
LOAD CURRENT VS TIME OF DAY
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• A 10% voltage reduction reduces heat output by 9.75%
• Overvoltage may cause burnouts.
• A 10% voltage reduction reduces light output by 30%
• A 10% overvoltage reduces lamp life 70%.
• Incandescent light bulbs wear out much faster at higher voltages
• Low voltage causes overheating, reduced starting and running torques and overload capacity
• Operating at 90% nominal, the full load current is 10 to 50% higher; temperature rises by 10 to 15%
• At a reduced voltage, the motor has reduced starting torque
• Low voltage on computers and televisions can cause them to become inoperative
Heating Element Lighting Motors Electronics
Why is Voltage Regulation Needed? The inability to supply proper voltage effects the following:
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Regulator Theory – Purpose Voltage Regulators: Solve voltage drop problem
+5%
--5%
Nominal
Voltage
OLTC R1
L1 L4 L2 L5 L3 L6 L7
Applied at Substation and midpoint of Feeder.
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Theory and Application
Medium Voltage Substations
(A) Regulation with OLTC Transformers
N.C.
N.C.
N.O. OLTC #1
OLTC #2
(B) Bus Regulation
Non-OLTC
(C) Feeder Regulation
Non-OLTC
SVR = Step-Voltage Regulator
3 - 1 SVRs f
3 - 1 SVRs f
Methods of Regulation
3 - 1 SVRs f
3 - 1 SVRs f
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• Regulate individual phases • Separate regulation from voltage transformation • Fast change out • Maintenance will not disrupt service • Standardized product • Readily Available vs sub transformer LTs
Why Voltage Regulators vs. LTC?
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• LTC ratings go beyond VR ratings
• Some prefer 3Ph Ganged Operation for dedicated 3Ph Loads
• Footprint
Why LTC vs. Voltage Regulators?
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What is a Voltage Regulator?
• Voltage Regulator - A device which will provide a constant voltage output under varying input voltages and load currents
• By standards, regulates +10% voltage and –10% voltage. • Total of 33 steps; = 5/8% voltage per tap. • 16 steps in the Raise direction, 16 steps in
the Lower direction, and one Neutral position.
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Three Basic Parts of a Voltage Regulator
• Autotransformer - A transformer in which part of one winding is common to both the primary and secondary windings
• Load Tap Changer - A switch designed to work under load to change the configuration of a transformer coil
• Voltage Regulator Control - A control which senses the system and automatically commands the tap changer.
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N 1 2 3 4 5 6 7 8
1.25%
L
SL
S
SHUNT WINDING
CONTROL
SERIES WINDING
TYPE A REGULATOR
POTENTIAL TRANSFORMER
REVERSING SWITCH
CURRENT X-FORMER
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Type A Design – “Straight”
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N 1 2 3 4 5 6 7 8
1.25%
SL
S
SHUNT WINDING CONTROL
SERIES WINDING
CONTROL WINDING
TYPE B REGULATOR
REVERSING SWITCH
CURRENT X-FORMER
L
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Type B Design – “Inverted”
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Differences from Customer’s Point of View
Type A verses Type B Differences
1. No difference in external connections or operation
2. Type B Regulation Range is +10% and -8.3%. Type A Regulation Range is +10% and -10%
3. It is okay to 3 phase bank a mix of Type A & Type B units
4. If paralleling, place the affected units in the Neutral position during the switching operation. Having them on the same step other than Neutral can generate circulating current between the banks due to voltage differences caused by differences in regulation between a Type A and Type B.
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• Pressure Relief Device Rating and Location Defined • Venting pressure = 34.5 kPa (5 psig) and flow of 50 Standard Cubic Feet per Minute SCFM • Located on the tank above the 110 °C top fluid level, as determined by the manufacturer's calculation.
It shall not be located in the quadrant of the tank that contains the control device. • Short Circuit Requirement Revised
• First Cycle Asymmetrical Peak increased to 2.60 from 2.26 for ratings greater than 165 kVA. • Maximum short circuit current changed from 20,000 amps to 16,000 amps. Design must meet 25 times
the rating or 16,000 maximum, whichever is less. • Nameplate Info Additions
• Symmetrical short circuit withstand ampere rating with time duration • Tap changer model • Ratio of load current to switched current (if series transformer is present)
• Support Lugs (Hanger Bracket) Requirements • Support lugs for pole mounting shall be provided for ratings 288 kVA and less, with rated line current of
328 amps or less. • Substation voltage regulators shall be arranged for rolling in two directions: parallel to and right angles
to one side of the voltage regulator. Bases for substation mounting shall be provided for 165 kVA and higher.
• Bushing Terminals Requirements Added • 4-hole spade terminals to be provided on current ratings above 668 amps
IEEE C57.15-2009 (IEC 60076-21)
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Given: 10 MVA, 3f transformer, 13.2 kV system voltage, grounded wye
Find: The proper regulator rating to use…...
Regulator Sizing
• Watch the units! 10 MVA = 10,000 KVA • For the regulator current rating:
Line current = Transformer size
VL−L× 3=
10,000kVA
13.2kV×1.732= 438 A
• For Regulator kVA Rating:
kVA rating = 𝑉𝐿−𝐺 × 𝐼 × % 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 7.62 𝑘𝑉 × 438 × 0.10 = 333 𝑘𝑉𝐴
• Choose standard rating from tables
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Single Phase Voltage Regulators
• Self contained • +/- 10% regulation in 32- 5/8%
steps • 55/65 °C average winding rise
(12% more capacity) • 25 to 2000 kVA (pad 875 A) • 2400 V to 34500 V (60-200 BIL) • Mineral oil or FR3 • Fan cooling option (33% more
capacity) • Substation, pole and pad mounted
designs
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Padmount Voltage Regulator
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Basic Control Settings Function Codes
• FC 1 - Set Voltage • FC 2 - Bandwidth • FC 3 - Time Delay • FC 4 – LDC Resistance • FC 5 – LDC Reactance • FC 39 - Source Side Calculation
• FC 140 Regulator Type • FC 41- Regulation Configuration • FC 42 - Control Operating Mode • FC 43 - Systems Voltage
(Nominal) • FC 44 - PT Ratio • FC 45 - CT Ratio • FC 49 - Tap Changer Type
• FC 50 - Clock • FC 143- Time Format • FC 142- Date Format
• FC 56 - Reverse Sensing Mode • FC 69 - Auto Blocking Status • FC 70 - Voltage Reduction • FC 80 - Voltage Limiter Mode
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Set Voltage
• The voltage level (on 120V base) to which the control will regulate
• Settable for both forward & reverse power flow
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Bandwidth
• The total voltage range around the set voltage which the control will consider acceptable
• Acceptable voltage range defined as: Range = SV +/- 1/2 BW
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Time Delay
• The number of seconds the control waits, from the start of an out-of-band condition, before initiating a tap change
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Time Delay
30 SECONDS
120
122
124
126
128
118
116
114
112
BANDWIDTH
TIME
VO
LTA
GE
SE
T P
OIN
T
Given: TD = 30
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Cascading Regulators
3-phase LTC
transformer TD = 30 SEC
SVR TD = 45 SEC
SVR TD = 45 SEC SVR
TD = 45 SEC
SVR TD = 75 SEC
SVR TD = 60 SEC
SVR TD = 60 SEC
Rule 1: Each succeeding regulator in series down line from the source requires a longer time delay Rule 2: The minimum time delay from one regulator to the next in cascade is 15 seconds
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Voltage Profile Without LDC
120
124
128
116
112
VOLT
AG
E
Minimum
DISTANCE FEEDER
voltage
voltage Maximum
Max. load
Min. load
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Line Drop Compensation • Control compensates for line losses – load, resistance and
impedance are considered • Dialing in line drop compensation moves the set voltage point
from the load bushing to the ‘Load Center’. VR > 0, and VX > 0
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Regulator - Capacitor Comparison
120
124
128
116
112
VO
LTA
GE
O
n Li
ne
DISTANCE FEEDER
R C
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Coordination w/Capacitors
• Any capacitor on the source side of a regulator does not affect regulator settings, as current through the line drop compensator is proportional to load current
• Any capacitor at the load center of a regulator (or beyond) does not affect regulator settings as current through the line drop compensator is proportional to load current
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Coordination w/Capacitors
• A regulator with capacitors located between the regulator and the load center must have it’s set voltage adjusted to compensate for additional voltage drop due to capacitor current flowing back to the source
• Only applies if LDC setting are used
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Reverse Sensing Mode
• Reverse Sensing Mode defines power flow condition settings • Reverse Sensing Mode Options
• Locked Forward (default setting) • Locked Reverse • Reverse Idle • Bi-directional • Neutral Idle • Co-generation • React Bi-directional
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When DG generates power that does not meet the load demand, DG will offset current through the VR and may cause VR to tap down, considering this situation as light loading
Load Side
R X
DG
When DG generates power that exceeds the load demand, some power is exported back to the power system. In this case, DG may increase current through the VR and cause VR to tap up, considering this situation as heavy loading. This may occur when the VR source voltage is near ANSI upper limit. As a result, voltage at the load may be excessive
DG Interactions with Voltage Regulators
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• When DG generates real power that does not meet the local load demand, some real power is provided by the power system. The VR will regulate voltage at the DG location in Forward Mode
• When DG generates real power that exceeds the load demand, some real power is exported back to the power system. However, the VR will not reverse direction and will continue to regulate voltage on the DG side
Substation
DG
Regulated voltage during forward or reverse power flow
Customer Load
Co-Generation Mode
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Substation
Substation
P, Q
P, Q
Open
Closed
When one source is lost, power flow will change and some VRs should change direction of the voltage regulation
Substation
Circuit Breaker
Tie Recloser N.O.
Voltage Regulator
Substation
Circuit Breaker
P, Q
P, Q
Direction of Voltage Regulation
DG DG
Why Co-Generation Mode may not be suitable for Loop Scheme applications?
Co-Generation Mode
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• DG operates with constant power factor mode, consuming some reactive power from the system. The VR controls voltage on its load side (DG side)
• The VR controls voltage on its load side irrespective of the real power flow that can be in both directions depending on the DG operation
Direction of voltage regulation during normal operation (Tie Recloser Open)
Source 1
DG
CB1 Closed
CB2 Closed
Tie Recloser Open
Q P
Source 2
Q
P
Reactive Bi-Directional Mode
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• When the Tie Recloser is closed and CB1 open, the reactive power through the VR will
change. When the VR detects the reactive power change, it will change the direction of the voltage regulation and will regulate voltage on the CB1 side
Source 1
DG
CB1 Open
CB2 Closed
Tie Recloser Closed
Q P
Source 2
Q
P
Direction of voltage regulation during Loss of Source 1 (CB1 Open)
(Tie Recloser Closed)
Reactive Bi-Directional Mode
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Solar Field Application
• Application: Need to be able to react to a 12-20% drop in utility voltage and correct it to 12% in less than 5 seconds.
• Solution: Utilize voltage limiting threshold to establish limits to initiate quick response to bring voltage back within threshold with minimal time delay
90
95
100
105
110
115
120
125
130
Volta
ge
Time (s)
Response to Undervoltage
Voltage setting
Upper Band
lower band
Actual Voltage
Lower Voltage limit
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Voltage Limiting
• Places a high and/or low limit on the output at the load bushing
• Highest priority of all operating functions • Options
• Off • High limit only; then requires High Limit Value • High & Low limits; then requires High and Low
Limits Values. • Default value = Off
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Voltage Limiter Response
Time Delay = 30 Seconds
2s delay between tap changes High Limit + 3 volts
c=0 c=10 (CL-6)
c=30
Time Delay counter (C) activated
High Limit
Low Limit + 3 volts
Low Limit
Low Bandwidth Edge
Set Voltage
High Bandwidth Edge
C is adjustable on CL-7
Response delay between
tap changes adjustable on CL-7
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INSTALLATION & OPERATION
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Regulator Installation • Ground the regulator tank AND the control
cabinet.
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Connections
S
L
SL
A
B
CN
Source
Disconnect
SeriesLightningArrester
Bypass Switch
ShuntLightningArrester
L
S SL S
L
SL
Bypass Switch Phase A Phase B Phase C
S
L
SL S
L
SL
Disconnect Switches
S
L
SL
Disconnect Switch
Bypass Switch Phase A Phase B Phase C
S
L
SL S
L
SL
4 Wire grounded wye: • 3 regulators required • ± 10% regulation
3 Wire open delta: • 2 regulators required • ± 10% regulation
3 Wire closed delta: • 3 regulators required • ± 15% regulation
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Paralleling Regulators
2 situations to consider :
• Continuous Parallel operation (in substation)
• Tying Feeders through N.O. point (or with Bus Tie switch)
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Paralleling Regulators
V
Simplified Diagram – 2 Voltage sources, 2 Impedances
V
Must have: • Same %Z
• Same turns ratio
Reactive Circulating Current
Regulators must use a “Leader-Follower” control setup
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Paralleling Regulators
Tying Feeders through a N.O. switching operation
R R
How do you set the Regulators ? Block Regulators (at least one) -Match Tap position? What tap? -Match Voltage? Where? -Impedance is your friend
N.O.
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Bypassing a Regulator
Definition: Bypassing means installing a regulator or removing a regulator from service.
Installing or removing the regulator with the tap changer off neutral will short circuit part of the series winding! Before bypassing, the regulator must be in neutral.
Warning! !
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Prior to Bypassing Place the regulator in neutral position A minimum of four indications are recommended
for neutral determination.
– Neutral lamp is “on” continuously
– Verify the tap position of the control indicates Neutral
– Position indicator is in neutral position
– Verify that there is no voltage difference between the S and L bushings
Tap Position 0
At Limit
P.I. ADD-AMP -16, 16
Tap Position 0
At Limit
P.I. ADD-AMP -16, 16
Bypassing a Regulator
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Theory and Application
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BYPASSING 1 step = 5/8% = .00625
Base voltage
Voltage per step
120 2400 4800 7200 7620 12000 14400 19920
.75 15 30 45 48 75 90 125
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Take action to prevent the tap changer motor operation
• Power switch is OFF
• ‘Auto/Off/Manual’ switch is OFF
• Remove motor fuse
• V1 & V6 knife switches are OPEN
Prior to Bypassing Bypassing a Regulator
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Bypassing Regulator Connected Line-to-Ground (GY)
Source Load
Phase A
Neutral
Bypass
Disconnect Disconnect
SL
L S
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Bypassing - Remove Procedure Regulator Connected Line-to-Ground (GY)
Source Load
Phase A
Neutral
SL
L S
S-DIS L-DIS
B
Start 1 2 3 B O C C C
S-Dis C C C O L-Dis C C O O
Step 1 is Critical Operation.
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Bypassing Regulator Connected Line-to-Line (Delta)
Source Load
Phase A
Phase B
Bypass
Disconnect Disconnect
Disconnect
S L
SL
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Bypassing - Remove Procedure Regulator Connected Line-to-Line (Delta)
Source Load
Phase A
Phase B
B
S-DIS
S L
SL
L-DIS
SL-DIS
Start 1 2 3 4 B O C C C C
SL-Dis C C C C O S-Dis C C C O O L-Dis C C O O O
Step 1 is Critical Operation.
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Regulators
• Questions??